• 대한기계학회논문집A
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• 제26권1호
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• pp.55-60
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• 2002

For the development of a new creep test technique, the availability of SP-Creep test is discussed for 1Cr-0.5Mo boiler header material. And some results are also compared with those of 2.25Cr- 1Mo steel which widely uses as boiler superheater tube. The results can be summarized as follows. The load exponents(n) obtained by SP-Creep test for 1Cr-0.5Mo steel are decreased with increasing creep temperature and the values are 15.67, 13.89, and 17.13 at 550$^{circ}C$ ,575$^{circ}C$ and 600$^{circ}C$, respectively. The temperature dependence of the load exponent is given by n = 107.19 - 0.1108T. This reason that load exponents show the extensive range of 10∼16 is attributed to the fine carbide such as M$_{23}$C$_{6}$ in lath tempered martensitic structures. At the same creep condition, the secondary creep rate of 1Cr-0.5Mo steel is lower than the 2.25Cr-1Mo steel1 due to the strengthening microstructure composed by normalizing and tempering treatments. Through a SEM observation, it can be summarized that the primary, secondary, and tertiary creep regions of SP-Creep specimen are corresponding to plastic bending, plastic membrane stretching, and plastic instability regions among the deformation behavior of four steps in SP test, respectively.y.

• 한국구조물진단유지관리공학회 논문집
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• 제23권4호
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• pp.137-144
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• 2019

취성재료인 탄소섬유보강폴리머(CFRP)의 시편시험에서 총변형량과 유효길이로서 유도되는 환산변형률을 도입하고, 환산변형률의 장점을 기술하였다. 일반적으로 재료의 인장물성을 결정하기 위해 스트레인 게이지 측정값을 사용하지만, 취성특성을 가지는 CFRP에서는 항상 유효한 것은 아니다. 그 이유는 취성재료에서는 응력재분배를 할 수 없으며, 스트레인 게이지의 측정값은 국부거동만을 나타기 때문이다. 따라서 환산변형률은 취성재료의 인장인장특성의 평균값을 측정하고 변형률과 측정값을 검증하는 보조지표로서 효과적으로 사용될 수 있다. 또한 환산변형률은 1) 제작 오차(편차) 와 세팅 오차(정렬 불량)에 의해 발생하는 초기 내부 변형률에 기인한 영향과 2) 불균일 변형분포로 인한 부분파단 이후 거동을 명확히 가시화하는 장점이 있다.

• Earthquakes and Structures
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• 제17권2호
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• pp.163-173
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• 2019

For Special Concentrically Braced Frame (SCBF), it is common that the damage concentrates at a certain story instead of spreading over all stories. Once the damage occurs, the soft-story mechanism is likely to take place and possibly to result in the failure of the whole system with more damage accumulation. In this study, we use a strongback column which is an additional structural component extending along the height of the building, to redistribute the excessive deformation of SCBF and activate more structural members to dissipate energy and thus avoid damage concentration and improve the seismic performance of SCBF. We tested one-third-scaled, three-story, double-story X SCBF specimens with static cyclic loading procedure. Three specimens, namely S73, S42 and S0, which represent different combinations of stiffness and strength factors ${\alpha}$ and ${\beta}$ for the strongback columns, were designed based on results of numerical simulations. Specimens S73 and S42 were the specimens with the strongback columns, and S0 is the specimen without the strongback column. Test results show that the deformation distribution of Specimen S73 is more uniform and more brace members in three stories perform nonlinearly. Comparing Drift Concentration Factor (DCF), we can observe 29% and 11% improvement in Specimen S73 and S42, respectively. This improvement increases the nonlinear demand of the third-story braces and reduces that of the first-story braces where the demand used to be excessive, and, therefore, postpones the rupture of the first-story braces and enhances the ductility and energy dissipation capacity of the whole SCBF system.

• 대한토목학회논문집
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• 제9권3호
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• pp.125-131
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• 1989

도로포장(道路鋪裝)은 그 수명기간내(壽命其間內)에 다수(多數)의 반복하중(反復荷重)을 받는 데, 이 반복된 재하(재하)에 의해 영구변형(永久變形)과 피로파괴(疲勞破壞)가 발생하여, 포장(鋪裝) 공용성(供用性)이 저하(低下)된다. 따라서 높은 공용성(供用性)을 유지(維持)하려면, 포장(鋪裝)의 각부(各部)에서 이와 같은 문제(問題)의 발생(發生)을 막고, 포장(鋪裝)의 안정성(安定性)을 향상(向上)시키기 위해서는 노반(路盤), 노상(路床)에 대해서 반복재하에 따른 영구변형(永久變形)이나 피로파괴(疲勞破壞)의 문제(問題)를 해결하는 것이 중요하다. 이와 같은 관점(觀點)에서 본(本) 연구(硏究)는 $20kg/cm^2$의 7일 강도를 갖는 각각 시멘트량 92%와 18.3%인 사질토 soil-cement와 점성토 soil-cement에 있어서 반복하중(反復荷重)을 가하였을 때의 변형특성(變形特性)에 대해서 검토(檢討)하였다. 연구 결과, 사질토 soil-cement의 탄성계수는 점성토 soil-cementt 보다 크며, 반복횟수 $1{\times}10^3$회(回)까지 탄성계수가 감소하고, 그 후 $1{\times}10^5$회(回)까지는 증가하였다. 또한 일축압축강도(一軸壓縮强度)는 약 30% 정도의 강도증가(强度增加) 나타냈다.

• 한국해양공학회지
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• 제21권2호
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• pp.50-59
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• 2007

Steam generator tubes are degraded from wear, stress corrosion cracking, rupture and fatigue and so on. Therefore, the failure assessment of steam generator tube is very important for the integrity of energy plants. In the steam generator tubes, sometimes, the local wall thinning may result from severe degradations such as erosion-corrosion damage and wear due to vibration. In this paper, the elasto-plastic analysis was performed by FE code ANSYS on steam generator tubes with wall thinning. Also, the four-point bending tests were performed on the wall thinned specimens, and then it was compared with the analysis results. We evaluated the failure mode, fracture strength and fracture behavior from the experiment and FE analysis. Also, it was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the thinned area from FE analysis.

• Journal of Biosystems Engineering
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• 제19권1호
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• pp.17-21
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• 1994

This reasearch was performed to provide the fundamental intonation for the mechanization of Korean pine cone harvest when the shoot shearing method is adopted. Shear force and stress of pine cone shoots were measured and analyzed for this purpose. Samples are selected along their harvesting time and tested in 17 levels of shoot diameter from 10 to 26mm with 1mm increment. 1) Shear force-deformation characteristics showed that shoot reached its rupture point after 2 to 4 of bio-yield points. It was supposed that these multiple bio-yield points were caused by the discrete compression of wood parts which are composed of water, nutrient, resin, etc. 2) Required shear force to shear shoot was proportional to the square of shoot diamter, however, shear force for shoots of early harvesting time(Aug. 31) was proportional to the shoot diameter. Variance of shear force was increased as the harvesting time was delayed. Shear forces were distributed from 468N(Aug. 31, 12mm dia) to 4153N(Aug. 31, 26mm dia) disregarding the sampling date. 3) The average shear stresses by sampling dates were 744,822, and 883N/m2, respectively, and for the earlier shoot samples shear stress was quite smaller than the others. Shear stress was proportional to shoot diameter squared, and the effect of shoot diameter on the shear stress was decreased as harvesting time was delayed.

• Journal of Biosystems Engineering
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• 제20권2호
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• pp.141-150
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• 1995

땅콩을 대상으로 하는 각종 농산가공기계의 개발 및 최적 작동에 필요한 땅콩 자실의 물리적, 기계적 및 공기 역학적 성질에 대한 연구가 수행되었다. 영호, 올, P.I. 314817의 3 가지 품종에 대해 땅콩 자실의 형상, 각부 칫수, 진밀도, 산물밀도 및 종실율이 측정되었으며, 땅콩자실에 대해 압축실험을 실시함으로써 자실이 파괴될 때의 힘, 변형량, 그리고 단위 체적당 최대 흡수 에너지인 터프니스 계수를 측정하여 기계적 성질로서 제시하였다. 공기 역학적 성질로서는 땅콩 자실과 종실의 종말속도 및 항력계수가 측정되었다. 1. 땅콩 자실의 기하학적 형상은 수원체로 모형화할 수 있었다. 2. 진밀도는 땅콩 자실의 경우는 515-620 $kg/m^3$, 종실의 경우는 960-1,090 $kg/m^3$, 의 값을 보였다. 3. 대합면이 수평인 자세에서의 파괴력은 영호가 61.9 N, P.I. 314817은 71.5 N, 올 땅콩은 84.8 N였으며, 터프니스 계수는 각각 30, 43, 72 kN-$m/m^3$, 의 값을 보였다. 모든 품종과 함수율에서 파괴력과 터프니스 계수는 대합면이 수직인 자세에서보다 수평자세에서 더 큰 값들을 보였다. 4. 땅콩 자실과 종실의 평균 종말속도는 각각 8.7-9.9 m/s, 10.0-11.6 m/s 범위였다. 종말속도는 진밀도와 직선적인 관계가 있었으며 품종과 형상에 따른 뚜렷한 종말속도의 차이는 보이지 않았다.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2565-2571
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• 2020

Background: Understanding the behaviour of nuclear fuel claddings by conducting burst test on single cladding tube under simulated loss-of-coolant accident conditions and developing theoretical cum empirical predictive computer codes have been the focus of several investigations. The developed burst criterion (a) assumes symmetrical deformation of cladding tube in contrast to experimental observation (b) interpolates the properties of Zircaloy-4 cladding in mixed α+β phase (c) does not account for azimuthal temperature variations. In order to overcome all these drawbacks of burst criterion, it is reasoned that artificial intelligence technique may be a better option to predict the burst parameters. Methods: Artificial neural network models based on feedforward backpropagation algorithm with logsig transfer function are developed. Results: Neural network architecture of 2-4-4-3, that is model with two hidden layers having four nodes in each layer is found to be the most suitable. The mean, maximum, and minimum prediction errors for this optimised model are 0.82%, 19.62%, and 0.004%, respectively. Conclusion: The burst stress, burst temperature, and burst strain obtained from burst criterion have average deviation of 19%, 12%, and 53% respectively whereas the developed neural network model predicted these parameters with average deviation of 6%, 2%, and 8%, respectively.

• 대한기계학회논문집
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• 제14권5호
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• pp.1349-1355
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• 1990

By examining the fatigue deformation properties of 12% Cr rotor steel which has been proved to have high fatigue and creep rupture strength around 600deg. C, authors reviewed major fatigue life prediction models such as Manson, Langer and Morrow equations, and following results were obtained. (1) A simple life prediction model for 12% Cr rotor steel was obtained as follows : DELTA..epsilon.$_{t}$ =2.18+.sigma.$_{u}$ /E+ $N^{-0.065}$+ $e^{0.6}$ $N^{-0.025}$ This equation shows that fatigue life, N, can be easily determined when total strain range, DELTA..epsilon.$_{t}$ and ultimate tensile strength, .sigma.$_{u}$ are known by simple tension test on the given test conditions. (2) Life prediction equation with equivalent maximum stress, DELTA..sigma./2, corresponding maximum strain in one cycle at room temperature is as follows: DELTA..sigma./w=-7.01logN+96.69+96.69

• Safety and Health at Work
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• 제1권1호
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• pp.43-50
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• 2010

Objectives: The objective of this study was to investigate the effect of chain installation condition on stress distribution that could eventually cause disastrous failure from sudden deformation and geometric rupture. Methods: Fractographic method used for the failed chain indicates that over-stress was considered as the root cause of failure. 3D modeling and finite element analysis for the chain, used in a crane hook, were performed with a three-dimensional interactive application program, CATIA, commercial finite element analysis and computational fluid dynamic software, ANSYS. Results: The results showed that the state of stress was changed depending on the initial position of the chain that was installed in the hook. Especially, the magnitude of the stress was strongly affected by the bending forces, which are 2.5 times greater (under the simulation condition currently investigated) than that from the plain tensile load. Also, it was noted that the change of load state is strongly related to the failure of parts. The chain can hold an ultimate load of about 8 tons with only the tensile load acting on it. Conclusion: The conclusions of this research clearly showed that a reduction of the loss from similar incidents can be achieved when an operator properly handles the installation of the chain.